You could have a power supply problem. This is indicated by no voltage on the big rail caps (+- 35 v or higher to speaker ground). You check that with a DVM. I like DVM from tenma from newark & house brand from parts-express. The Harbor Freight meter my project leader had cost us 2 days work when it lied to us. Don't test power on with two hands. >24 v across your heart can stop it. Connect the negative of the DVM, analog VOM, oscilloscope, or sound probe, to the negative speaker jack. Use an alligator clip lead. Available in packs of 10 for ~$7 from parts-express.com . Available for $70 for 10 from pamona via newark, digikey, mouser. Don't wear jewelry repairing electronics. Current through a ring or bracelet can burn your flesh to charcoal. Wear safety glasses, parts can explode. Solder can splash especially when desoldering.
For music stoppage see post #4 & #13. You set the FM radio to input about 0.3 vac in the jack. You should have about 0.2 to 1 vac after the input transistor. About .5 to 20 vac after the VAS transistor. 1 vac or more out the output transistors. If signal is present at the junction of the two emitter resistors but stops at the relay, there you are.
New people often short one thing to another with a regular meter probe. This damages parts. You can probe more safely with a $50 oscilloscope probe, or with the VOM or sound probe, a pamona grabber. These can be bought with a banana plug on the other end to fit in a VOM socket. I'd say get the 1/8" stereo phono plug to dual RCA banana plug cable (for the radio) , the alligator clip leads, the pamona grabber test lead, maybe some solder, all on the first order to save freight.
If you are not committed to learning this hobby, fine. However 30-40 year old amps are full of rubber sealed capacitors that can leak out the water at any point. Professionals like the McIntosh service usually won't quote replacing all electrolytic caps at once. They like to replace "the one that is defective", leaving all the others to fail one at a time. How reliable are 30 year old tires? Same problem as rubber sealed caps. With one or two new caps your amp is broken all the time as the others fail one by one. As an amateur, you can replace them all one at time (followed by sound check to point out mistakes) so your amp performs like a new one for 10-30 years. I like long life capacitors, >3000 hours service life. I had to replace e-caps in my first hifi amp 4 times in my life, buying front shelf parts in a TV parts store. Too much work.
For music stoppage see post #4 & #13. You set the FM radio to input about 0.3 vac in the jack. You should have about 0.2 to 1 vac after the input transistor. About .5 to 20 vac after the VAS transistor. 1 vac or more out the output transistors. If signal is present at the junction of the two emitter resistors but stops at the relay, there you are.
New people often short one thing to another with a regular meter probe. This damages parts. You can probe more safely with a $50 oscilloscope probe, or with the VOM or sound probe, a pamona grabber. These can be bought with a banana plug on the other end to fit in a VOM socket. I'd say get the 1/8" stereo phono plug to dual RCA banana plug cable (for the radio) , the alligator clip leads, the pamona grabber test lead, maybe some solder, all on the first order to save freight.
If you are not committed to learning this hobby, fine. However 30-40 year old amps are full of rubber sealed capacitors that can leak out the water at any point. Professionals like the McIntosh service usually won't quote replacing all electrolytic caps at once. They like to replace "the one that is defective", leaving all the others to fail one at a time. How reliable are 30 year old tires? Same problem as rubber sealed caps. With one or two new caps your amp is broken all the time as the others fail one by one. As an amateur, you can replace them all one at time (followed by sound check to point out mistakes) so your amp performs like a new one for 10-30 years. I like long life capacitors, >3000 hours service life. I had to replace e-caps in my first hifi amp 4 times in my life, buying front shelf parts in a TV parts store. Too much work.
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Electrotanya has the MC-2500 service manual: https://elektrotanya.com/macintosh_mc2500.pdf/download.html
That is a free site but documents are frequently in hungarian or other language.
That is a free site but documents are frequently in hungarian or other language.